Polyolefin resins such as polyethylene or polypropylene have many of desirable properties for fabricating various articles and parts such as containers, mechanical parts, electric and eletronic parts, automobile parts and the like. These properties include, among others, high resistance to water and chemicals, electrical insulation property, high mechanical strength and high processability for fabrication. Polyolefins consist solely of carbon and hydrogen atoms and, therefore, inflammable. For use in a field of application that requires flame retardancy, a flame retardant is incorporated into the polyolefin resin.
Conventionally bromine-containing flame retardants have been used for this purpose. Most of such flame retardants, however, are not well compatible with the resin and tend to migrate to the surfaces of fabricated parts known as “bleeding” when incorporated in an amount sufficient to impart with a desired level of flame retardancy such as V-O of UL-94 standard. When migrated flame retardants deposit on the surfaces of parts as off-white crystals or powders, they are called “blooming”.
Bleeding and blooming are deleterious not only to the appearance of parts but also to the performance of devices and instruments in which such parts have been mounted.
Several attempts have been made to prevent bleeding and blooming. JP-A-04285647 discloses a flame retarded polypropylene composition including 2,2-bis[4-(2,3-dibromopropoxy)-3,5-dibromophenyl] propane and a benzylidene derivative of sorbitol or xylitol. JP-A-10182889 discloses a flame retarded polyolefin composition including a halogen-containing flame retardant and a polymer containing aromatic hydrocarbon monomer such as styrene. Because such substances are free of bromine, the bromine content and, therefore, the degree of flame retardancy of the entire flame retarded composition must be compromised when they are added in an effective amount to prevent bleeding and blooming satisfactorily. Co-addition of the benzylidene derivative of sorbitol and xylitol suffers from another problem of deposition or sticking on the inner surfaces of injection molds.